The present invention is related to brake apparatus for a railway vehicle and particularly to such brake apparatus as disclosed in U.S. Pat. No. 4,058,348, issued Nov. 15, 1977 to the assignee of the present invention, wherein a brake cylinder device is arranged to provide for storage of sufficient air as necessary to develop the desired brake forces without the need for conventional storage reservoirs.
In the above-mentioned patent, the brake cylinder device embodies a pair of tandem-connected pistons of unequal diameter. The larger power piston cooperates with the brake cylinder body to form on the respective opposite sides thereof a chamber for the storage of air supplied via the train brake pipe, while the smaller positioning piston cooperates with the cylinder housing to also provide on its opposite sides fluid pressure chambers.
A control valve device is operative in response to a reduction of the brake pipe pressure to connect the air stored in the chamber on one side of the power piston to the chamber formed on the corresponding side of the positioning piston to effect pressure equalization therebetween. A one-way check valve associated with the power piston provides for the pressure on the other side of the power piston to equalize with the reduced pressure on the one side thereof to prevent a pressure differential from developing across the power piston, as the positioning piston is actuated in response to the pressure acting thereon. In this manner, the power piston is shifted in an application direction in order to decrease the volume on the other side thereof, while concurrently the pressure in this chamber is reduced in some proportion to the brake pipe reduction. This creates a pressure differential across the power piston to produce the desired brake application forces. Inasmuch as the volume of this other chamber from which air is exhausted is reduced by movement of the tandem-connected pistons in a brake application direction, the desired pressure reduction therein is obtained with only a minimum amount of air loss, thus making possible the use of a normal sized brake cylinder for the additional purpose of a storage reservoir.
It should be apparent from the foregoing that in order to obtain optimum benefit of low air consumption, movement of the power piston to brake application position should occur prior to the exhaust of any air from the chamber formed on the other side of the power piston, so that the volume thereof is reduced to a minimum before any air is exhausted.